In classic wireless cellular telecommunication networks, each base station has an identifier like a physical cell identifier (PCID) for each of its cells or each sector of its cell or cells. The PCID characterises a cell or sector of the base station in the physical layer.
For example, the PCID is associated to two sequences, a first sequence named PSC sequence or Primary Synchronisation Signal (PSS) is transferred in the Primary Synchronisation Channel (PSC) and a second sequence named SSC sequence or Secondary Synchronisation Signal (SSS) is transferred in the Secondary Synchronisation Channel (SSC).
Three PSC sequences are available in the wireless cellular telecommunication network, each having good time auto-correlation properties.
In addition to PCID identification, the PSC sequences may be used for rough synchronisation and for channel estimation enabling coherent detection of the SSC sequence. In addition to PCID identification, the SSC sequences may be used for synchronisation refinement.
The three PSC sequences are quasi-orthogonal in order to ensure efficient time synchronisation for three different synchronised cells.
Hundred sixty eight SSC sequences are available in the wireless cellular telecommunication network, each having low cross-correlation with other SSC sequences.
According to the aforementioned example, the total number of PCIDs is then equal to five hundred and four.
The PCID is usually used to identify a cell and to characterise a code for scrambling data exchanged with mobile terminals.
By monitoring the received PCID signals strength from neighbouring base stations at a mobile terminal, the system can decide to hand-over the mobile terminal communication to the best signal strength base station.
Schematically, a mobile terminal reports measures and corresponding PCID to its serving base station. The base station decides that it's profitable to proceed to a hand-over of the mobile terminal to a target base station identified by a selected PCID. The base station transfers a hand-over request to the target base station. If the hand-over is accepted, resources are allocated at the target base station and the base station asks the mobile terminal to hand-over to the target base station. The mobile terminal attempts to connect to the target base station and the resource is freed at the source base station in case of success. A path switch is made to redirect data intended to the mobile terminal to the target base station.
Today, wireless cellular telecommunication networks are largely deployed but there are still some areas not covered by the base stations of the wireless cellular telecommunication network.
The access to the wireless cellular telecommunication network might not be possible for a mobile terminal located in a building, if the signals radiated by the base stations are too attenuated.
Particular wireless telecommunication devices, like home base stations or femto base stations or pico base stations, provide coverage areas at least within the buildings. Relays are also considered.
In a wireless cellular telecommunication network comprising a large number of home base stations, a base station may face a situation wherein under its coverage area, several home base stations transmit the same PCID. The neighbouring relation table is not anymore a one to one mapping between the PCID and the cell of the target base station or home base station. This situation is called PCID confusion as the source base station cannot uniquely identify, from a PCID, the cell of the target base station or home base station in a hand-over procedure.
In a network comprising a large number of home base stations, interference management is a critical issue. When the amount of home base stations becomes very important, situation may occur wherein classic Inter Cell Interference Coordination (ICIC) techniques cannot be used. The possibility to manage base stations interferences by groups may be necessary.